4,818 research outputs found
Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals
Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica
Magnetic properties of Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals
Magnetic properties were studied for the high quality Al-free orthorhombic
Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals (0<=x<=1.0) grown by the flux
method. An indication on the interaction between the Pr and Cu(2) magnetic
sublattices was found for Pr123. Different signs of magnetic anisotropy were
established for the Pr and Gd ions at low temperatures. It was also shown that
superconductivity reported by Zou et al. [Phys. Rev. Lett. 80 (1998) 1074] for
Pr123 single crystals grown by TSZF method seems to be connected with partial
substitution of Ba for the Pr-sites.Comment: 2 pages (LaTeX2e), 4 EPS figures, phbauth style file included. LT22
conference paper accepted to Physica
Current Tomography -- Localization of void fractions in conducting liquids by measuring the induced magnetic flux density
A novel concept of a measurement technology for the localization and
determination of the size of gas bubbles is presented, which is intended to
contribute to a further understanding of the dynamics of efficiency-reducing
gas bubbles in electrolyzers. A simplified proof-of-concept (POC) model is used
to numerically simulate the electric current flow through materials with
significant differences in electrical conductivity. Through an automated
approach, an extensive data set of electric current density and conductivity
distributions is generated, complemented with determined magnetic flux
densities in the surroundings of the POC cell at virtual sensor positions. The
generated data set serves as testing data for various reconstruction
approaches. Based on the measurable magnetic flux density, solving Biot-Savarts
law inversely is demonstrated and discussed with a model-based solution of an
optimization problem, of which the gas bubble locations are derived
A reliability assessment of physical vulnerability of reinforced concrete walls loaded by snow avalanches
Snow avalanches are a threat to many kinds of elements (human beings,
communication axes, structures, etc.) in mountain regions. For risk
evaluation, the vulnerability assessment of civil engineering structures such
as buildings and dwellings exposed to avalanches still needs to be improved.
This paper presents an approach to determine the fragility curves associated
with reinforced concrete (RC) structures loaded by typical avalanche
pressures and provides quantitative results for different geometrical
configurations. First, several mechanical limit states of the RC wall are
defined using classical engineering approaches (Eurocode 2), and the
pressure of structure collapse is calculated from the usual yield line
theory. Next, the fragility curve is evaluated as a function of avalanche
loading using a Monte Carlo approach, and sensitivity studies (Sobol indices)
are conducted to estimate the respective weight of the RC wall model inputs.
Finally, fragility curves and relevant indicators such a their mean and
fragility range are proposed for the different structure boundary conditions
analyzed. The influence of the input distributions on the fragility curves is
investigated. This shows the wider fragility range and/or the slight shift in
the median that has to be considered when a possible slight change in
mean/standard deviation/inter-variable correlation and/or the non-Gaussian
nature of the input distributions is accounted for
The Fueling Diagram: Linking Galaxy Molecular-to-Atomic Gas Ratios to Interactions and Accretion
To assess how external factors such as local interactions and fresh gas
accretion influence the global ISM of galaxies, we analyze the relationship
between recent enhancements of central star formation and total
molecular-to-atomic (H2/HI) gas ratios, using a broad sample of field galaxies
spanning early-to-late type morphologies, stellar masses of 10^(7.2-11.2) Msun,
and diverse stages of evolution. We find that galaxies occupy several loci in a
"fueling diagram" that plots H2/HI vs. mass-corrected blue-centeredness, a
metric tracing the degree to which galaxies have bluer centers than the average
galaxy at their stellar mass. Spiral galaxies show a positive correlation
between H2/HI and mass-corrected blue-centeredness. When combined with previous
results linking mass-corrected blue-centeredness to external perturbations,
this correlation suggests a link between local galaxy interactions and
molecular gas inflow/replenishment. Intriguingly, E/S0 galaxies show a more
complex picture: some follow the same correlation, some are quenched, and a
distinct population of blue-sequence E/S0 galaxies (with masses below key
transitions in gas richness) defines a separate loop in the fueling diagram.
This population appears to be composed of low-mass merger remnants currently in
late- or post-starburst states, in which the burst first consumes the H2 while
the galaxy center keeps getting bluer, then exhausts the H2, at which point the
burst population reddens as it ages. Multiple lines of evidence suggest
connected evolutionary sequences in the fueling diagram. In particular,
tracking total gas-to-stellar mass ratios within the diagram provides evidence
of fresh gas accretion onto low-mass E/S0s emerging from central starbursts.
Drawing on a comprehensive literature search, we suggest that virtually all
galaxies follow the same evolutionary patterns found in our broad sample.Comment: 24 pages, 11 figures (table 4 available at
http://user.physics.unc.edu/~dstark/table4_csv.txt), accepted for publication
in Ap
INTEGRAL probes the morphology of the Crab nebula in hard X-rays/soft gamma-rays
Aims. We use the IBIS/ISGRI telescope on-board INTEGRAL to measure the
position of the centroid of the 20-200 keV emission from the Crab region.
Methods. We find that the astrometry of the IBIS telescope is affected by the
temperature of the IBIS mask during the observation. After correcting for this
effect, we show that the systematic errors in the astrometry of the telescope
are of the order of 0.5 arcsec. In the case of the Crab nebula and several
other bright sources, the very large number of photons renders the level of
statistical uncertainty in the centroid smaller or comparable to this value.
Results. We find that the centroid of the Crab nebula in hard X-rays (20-40
keV) is shifted by 8.0 arcsec with respect to the Crab pulsar in the direction
of the X-ray centroid of the nebula. A similar shift is also found at higher
energies (40-100 and 100-200 keV). We observe a trend of decreasing shift with
energy, which can be explained by an increase in the pulsed fraction. To
differentiate between the contribution of the pulsar and the nebula, we divide
our data into an on-pulse and off-pulse sample. Surprisingly, the nebular
emission (i.e., off-pulse) is located significantly away from the X-ray
centroid of the nebula. Conclusions. In all 3 energy bands (20-40, 40-100, and
100-200 keV), we find that the centroid of the nebula is significantly offset
from the predicted position. We interpret this shift in terms of a cut-off in
the electron spectrum in the outer regions of the nebula, which is probably the
origin of the observed spectral break around 100 keV. From a simple
spherically-symmetric model for the nebula, we estimate that the electrons in
the external regions of the torus (d ~ 0.35 pc from the pulsar) reach a maximal
energy slightly below 10^14 eV.Comment: 7 pages, 8 figures, accepted for publication in A&
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